The final staircase was removed from the earthquake-damaged Forsyth Barr building in central Christchurch today, allowing engineers close-up access to the empty stairwell to assess structural damage.

Several stairwells collapsed during the February 2011 quake, trapping office workers in the 18-storey building.

Seven stairwells stayed intact, but one fell in the December 23 aftershocks.

The remaining six were cut and lifted from the building in a four-month project that ended today.

Pace Project Management director Andrew Christian said there was no precedent for how to extract the staircases.

''You don't just go to Google and say 'how do you take stairs out of multi-storey buildings?' They were a fall hazard, so we couldn't actually get close,'' he said.

''It's taken about six to eight weeks to get them out [after a] couple of months working out how we were going to do it.''

The reinforced-concrete staircases weighed nearly nine tonnes each and had to be cut in half before being lifted out.

A purpose-built steel support structure was used to hold them in place while they were extracted via the building's roof.

''We cut a hole in the roof and then we had to support each stair,'' Christian said.

''We had to cut them in half because they were too heavy to take out the top, so we had to support them at each level as we took them out.''

A building inspection would start tomorrow and take six weeks, he said.

''The engineers [Holmes Consulting] obviously need to get close to the stairwells because that's where the main structure of the building is to inspect, but they haven't found anything untoward yet,'' he said.

''It could still come down, but it's...looking likely it will be economically repairable.''

The staircases were the subject of much scrutiny when the building was discussed at the Canterbury earthquakes royal commission hearing in February.

They were not part of an inspection after the September 2010 quake and the commission heard that debris was wedged into ''seismic gaps'' meant to give the stairs space to move in a quake.